The industry trend goes towards high capacity MSC servers which are also scalable. A typical architecture for such a system is a blade cluster structure with a plurality of blades. Transmission lines that carry payload are terminated in media gateways and the switching of these resources is controlled by the MSC server. Gateways act as translation units to enable communication between disparate networks. By way of example, a gateway can connect telephone networks of one or more operators and it can connect asynchronous transfer mode networks (ATM networks) to IP networks or TDM networks.
A termination of a media gateway is a logical entity which is the source and/or the sink of media and/or control streams. Each termination has a unique identity, the termination ID.
A context is an association between a number of terminations. The context describes the topology (who hears/sees whom) and the media mixing and/or switching parameters if more than two terminations are involved in the association. A termination shall exist in only one context at a time. A context is created by adding the first termination (with ADD command or MOVE command) and it is released by removing/subtracting the last termination (with SUBTRACT command or MOVE command).
Ephemeral terminations are better suited to a multi-blade architecture. The seizure of terminations is coordinated by the media gateway. There is no need for inter blade coordination on the MSC server side.
A change of the number of blades has no impact on the configuration of the other nodes. By way of example, additional processing capacity can be gained by installing new blades without operational intervention in other nodes. This basically requires a control association between the MSC blade cluster and the media gateway and makes multiple virtual media gateway configurations in a physical media gateway obsolete.
H.248 (or IETF name Megaco, Media Gateway Control Protocol) is for control of elements in a multimedia gateway and is used as a control protocol between the media gateway and the media gateway controller that may be provided in a mobile switching center.
A wildcard mechanism is known using two types of wildcards with termination IDs. These two wildcards are “ALL” and “CHOOSE”. The former “ALL” is used to address multiple terminations at once while the latter “CHOOSE” is used to indicate to a media gateway that it should select a termination satisfying a partially specified termination ID. This allows for instance that a media gateway controller instructs a media gateway to choose an ephemeral termination.
In case of a blade failure and in order to allow an efficient use of resources a termination controlled by a failed blade needs to be recovered in an efficient way.
Recovery of ephemeral terminations can be done by connecting a different virtual media gateway to each blade, with different control associations. In case of outage of a blade all terminations linked to the control association are recovered. Another way to recover ephemeral terminations in a media gateway after outage of a blade with loss of calls controlled by that blade is to rely on mechanisms defined in ITU-T H.248.36 “Hanging termination detection package”. This package offers a possibility for a media gateway to notify the server for any termination lasting longer than a predefined timer. The timer value is much longer than the mean holding time, where 90 s is a typical value.
In case of a TDM (time division multiplex) termination, the recovery has to be done one by one. TDM terminations are required to be accessible by all blades, otherwise, pre-partition of TDM termination can limit the efficiency of TDM termination resources at single blade outage and may violate certain ISUP/TUP standards which require certain patterns to assign TDM terminations to avoid collision. The result is that the TDM termination to be subtracted is not in a continuous range of termination ID or any fixed pattern and a wildcard mechanism would not be possible.
In the case of a configuration using virtual media gateways, it's possible to recover all terminations linked with the control association, but the possibility to share TDM terminations between different blades does not exist.
The mechanism to recover terminations after outage of a blade with loss of calls controlled by that blade such as the “hanging termination solution” has the drawback that long recovery time is required and that a large amount of messages needs to be exchanged between the MSC server and the media gateway.